Electrophoresis of, for example, samples of DNA fragments are commonly performed in a gel matrix of either agarose or acrylamide. In the case of agarose, the gel is usually poured while molten on to a horizontal glass plate on which it forms a layer which then sets; and in order to handle a plurality of samples simultaneously a "comb" having a row of protruding teeth or pegs is positioned so that the pegs project into the agarose layer while it sets. When the agarose layer has set, the comb is removed to leave a row of holes or wells in the layer adjacent one edge of the plate. These wells can then be loaded with samples which are then subjected simultaneously to electrophoresis by applying a voltage from end to end of the agarose layer so as to form a corresponding number of parallel electrophoresis tracks each extending from a respective one of the loaded wells towards the other end of the plate. In order to accommodate a larger number of samples than can conveniently be loaded into a single row of wells, the comb may be formed with a second row of pegs to form a second row of wells in the agarose, the second row being spaced from the first, and also from the other end of the plate, by a distance greater than the desired length of the electrophoresis tracks which are to be obtained.
In the case of an acrylamide gel layer, the open-faced preparation method used for agarose is not suitable, because acrylamide does not polymerise in the presence of air. It is therefore usual to prepare the acrylamide as a sandwich layer between two glass plates and, since neither major face of the layer is accessible, to form the wells in one end edge of the acrylamide layer. Electrophoresis is then carried out with the sandwich vertical, and its edge in which the wells are formed as its upper edge, so that samples can be loaded into the wells. It would not be practical in such a case to provide a spaced additional row of wells to enable a larger number of samples to be handled simultaneously. Acrylamide does, however, provide higher resolution of samples and, other considerations being equal, would be preferred to agarose.
There is a need for an electrophoresis gel-matrix layer which enables larger numbers of samples to be handled simultaneously than is possible with either of the known multiple-well plates described above, and it is an object of the invention to provide an improved electrophoresis gel-matrix layer which achieves this.